When packer sealing elements are axially compressed to grow in radial dimension to the surrounding tubular they have a tendency to axially extrude. As a result backup rings are used to close the extrusion gap to maintain the integrity of the sealing element. Typically backup rings are made to overly the sealing element and are pushed out radially with the sealing element when axial compression of the sealing element takes place. To effectively accomplish this task the backup rings cannot be too stiff as they will leave gaps from the surrounding tubular wall through which parts of the sealing element will extrude. If the material is too soft the pressure in the sealing element can overcome the backup ring and extrude. Another concern of designs that overly the sealing element is what happens if the packer is to be released. Rings that are too stiff could remain extended against the surrounding tubular wall even after the sealing element is relaxed. As a result such rings can become twisted and mangled and could cause the released packer to stick in the hole which requires an expensive milling out.
Alternative designs have been developed to the overlapping design that use a tapered ring that is wedged out as the seal is axially compressed. Such designs are illustrated in US 20130192853; U.S. Pat. Nos. 5,701,959; and 5,540,279 (FIG. 5). The more traditional overlay design is seen in U.S. Pat. Nos. 5,961,123; 8,083,001 and 6,695,051. Of general interest in the area of backup rings is U.S. Pat. No. 4,105,215.
The present invention uses a folding or collapsing design for the backup rings that features a thinner wall at the bend location and a thicker wall at the opposed extremities. The preferred cross-sectional configuration is a V-shape where the legs extend toward the surrounding tubular and are thicker than at the fold where the legs are joined. In this way there is little resistance to folding and radial extension while placing the thicker walled legs adjacent the surrounding tubular. The V-shape can also be inverted putting the legs near the mandrel and the junction of the legs toward the surrounding tubular. In the latter case the junction can be made thicker than the legs or the other way around. The folding creates radial extension to the surrounding tubular for an effective extrusion barrier. The design also releases more easily when the seal is allowed to collapse. These and other features of the present invention will be more readily apparent to those skilled in the art from a review of the detailed description of the preferred embodiment and the associated drawings while appreciating that the full scope of the invention is to be determined by the appended claims.